Docker-compose make 2 microservices (frontend+backend) communicate to each other with http requests

Question

I have 2 microservices: frontend with next.js and a backend with node.js from where I fetch data via REST-APIs from the frontend.

I now have the problem, that my 2 services don't seem to communicate directly to eachother, the thing is, it works when I fetch the data at the beginnning with the getinitialProps() Method with the fetch-API. My server-side frontend finds the backend via its service-name. However, when I am doing a http-request from the client to the backend (e.g via browser form inputs). It cannot find the backend anymore? Why is that?

here is my docker-compose.yml:

version: '3'

services:
  dcbackend:
    container_name: dcbackend
    build:
      context: ./dcbackend
      dockerfile: Dockerfile
    image: dcbackend
    hostname: dcbackend
    ports:
      - '7766:7766'

  dcfrontend:
    container_name: dcfrontend
    build:
      context: ./dcfrontend
      dockerfile: Dockerfile
    image: dcfrontend
    volumes:
      - /app/node_modules
      - ./dcfrontend:/app      
    hostname: dcfrontend
    ports:
      - '6677:6677'

Here is one of my browser-client side methods to send data to the backend (via the browser, my url is http:dcbackend... so normally it should find the other docker environment where the backend is, but it does not...

    if (environment == 'dev') {
  url_link = `http://localhost:${port}`;  
} else {
  url_link = `http://dcbackend:${port}`;
}

let doublettenListe_link = `${url_link}/doubletten/`;

 finishDocumentHandler = (anzeige,index) => {
    let thisDocumentID = anzeige.id;
    const requestOptions = {
        method: 'PUT'
    };

    fetch(doublettenListe_link + thisDocumentID, requestOptions)
    .then((response) => {   
        this.setState({finishSuccess: 'Dubletten in Datenbank eintragen erfolgreich!'});
        this.setState({finishFail: ''});
        this.processDocumentArray(index);
        console.log(response);
    })
    .catch((error) => {   
        this.setState({finishSuccess: ''});  
        this.setState({finishFail : `Error beim Erzeugen des Eintrags! Eintrag wurde nicht in Datenbank gespeichert. Bitte prüfen, ob der Server läuft. ${error}`});
    }); 
  }  

Response from network tab from my request is:

Request URL: http://dcbackend:7766/doubletten/304699981
Referrer Policy: no-referrer-when-downgrade
Provisional headers are shown
Access-Control-Request-Method: PUT
Origin: http://localhost:6677
Referer: http://localhost:6677/
User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/73.0.3683.103 Safari/537.36

does it have something to do with docker-configuration, or with CORS() or with anything else? I can't do a client http request to backend, however, the initial fetch from the backend to get some data works...

Answer 1

You have to separate the server side and the client side requests. You need to use your host address for the client side requests (eg. http://localhost:7766), because your browser will not be able to reach the backend via docker alias.

You can define the server-only and public runtime config with next.config.js.

For example:

// next.config.js
module.exports = {
  serverRuntimeConfig: {
    // Will only be available on the server side
    apiUrl: 'http://dcbackend:7766'
  },
  publicRuntimeConfig: {
    // Will be available on both server and client
    apiUrl: 'http://localhost:7766'
  }
}

Then you need get the apiUrl from nextjs with getConfig()

// pages/index.js
import getConfig from 'next/config';

const { serverRuntimeConfig, publicRuntimeConfig } = getConfig();

const apiUrl = serverRuntimeConfig.apiUrl || publicRuntimeConfig.apiUrl;

const Index = ({ json }) => <div>Index</div>;

Index.getInitialProps = async () => {
    try {
       const res = await fetch(`${apiUrl}/doubletten/304699981`);
       const json = await res.json();
       return { json };
    } catch(e) {
       console.log('Failed to fetch', e);
       return { json: null };
    }
}

export default Index;